1. Field of the Invention
The present invention relates to an electrophotographic photoconductor for use in an image-forming apparatus such as an electro-static copying machine or a laser printer, and more particularly to an electrophotographic photoconductor utilizing perylene pigment as a charge generating material and a method for preparing the same.
2. Description of the Prior Art
A coating solution for a photoconductor is prepared by dissolving binding resin in a solvent and then mixing a charge generating material, a charge transport material, etc., therein. This coating solution is applied onto a conductive substrate in lamination or monolayer, and then dried to prepare a photoconductor. The photoconductor obtained by the use of the coating solution has the advantages of high capability of forming a film and high productivity because it can be produced in a coating process. The photoconductor has further advantages in that the selection of pigment, etc., may freely control the photosensitive property, etc. Accordingly, the photoconductor has been studied in many respects.
As a charge generating material present in the aforesaid coating solution, perylene pigment may be used. This perylene pigment can be obtained usually by reacting perylene tetracarboxylic acid anhydride with an amine compound.
An electrophotographic organic photoconductor using perylene pigment thus synthesized requires properties such as sufficient sensitivity and repeatability to be a photoconductor. As a factor which controls the properties of the photoconductor, the properties such as the purity, the type of crystal, and the particle size of the pigment have been studied.
These properties of the pigment affect not only the aforesaid properties of the photoconductor but also the stability of preserving a coating solution, so the crude pigment after being synthesized requires various treatments immediately.
The applicant of the present invention filed an application regarding a monolayer positively charged photoconductor having excellent repeatability and aging property utilizing perylene pigment as a charge generating material in Japanese Laid-Open Patent Publication No. 63-85750. In this publication, the perylene pigment is prepared in the following manner.
The synthesized perylene pigment is dissolved in sulfuric acid, after which the sulfric acid solution is dropped into ice water to prepare .alpha. type perylene pigment. Thereafter, the resulting dispersion is washed with water to prepare a crude material. To the crude material is added nitrobenzene or dichloromethane to prepare .beta. type perylene pigment. Then, the resulting .beta. type perylene pigment solution is treated in a ball mill to prepare .alpha. and .beta. type perylene pigment. Thereafter, to the resulting mixture is added methanol to be filtered, and then the filtered substance is dried and classified to obtain perylene pigment having a particle size in the range of 0.05 .mu.m to 0.1 .mu.m.
However, when a coating solution for a photoconductor is prepared by the use of the perylene pigment obtained by the above method as a charge generating material, the particle size of the perylene pigment increases due to the crystal growth in the coating solution. As a result, when copying by the use of the resulting photoconductor, there occurs a deficiency in that the surface potential (residual potential) of the photoconductor becomes high after exposure, which markedly occurs in the case of a monolayer photoconductor.